Heating substrates during the growth of thin films in vacuum chambers, such as electronic and optical films, often is difficult. The heaters in systems designed for thin-film growth by evaporation, ion-sputtering, molecular beam epitaxy, and laser ablation, for example, are often the most fragile and failure-prone subsystems in the process. The heater deficiency has been prevalent even though most films are grown either under high-vacuum conditions or in a partial pressure of an inert gas such as argon. Such inert atmospheres are usually the best environments for maximizing the lifetime of heating wires and fixtures.
The discovery and continuing research into high-temperature superconducting thin films has put additional constraints on the operation of vacuum system heaters primarily because the new superconductors, such as YBa.sub.2 Cu.sub.3 O.sub.7, Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8, and Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10, are oxides. These oxides are impossible to make in a true high-vacuum environment since molecular oxygen (O.sub.2) at partial pressures of at least 10 milliTorr must be present during growth to foster the formation of these compounds in the proper crystalline phase. For example, oxygen partial pressures up to 0.5 Torr, and temperatures in excess of 700.degree. C. are typical deposition conditions used for the growth of these materials. Following deposition, the films are usually cooled from the growth temperature at oxygen pressures of a few hundred Torr. An anneal at 400.degree.-500.degree. C. in one atmosphere of oxygen completes the process. Oxygen partial pressures over 10.sup.-4 Torr usually cause severe problems for most heater materials heated to such high temperatures.
In many contemporary vacuum-chamber heaters, heat is transferred to the substrate by infrared radiation. The source of infrared radiation may be a sealed quartz lamp, see R. J. Mattauch, Rev. Sci. Instrum, vol. 43, 1972, p. 148, or heated tungsten or platinum windings, see D. M. Hoffman and F. J. Tams III, Journal of Vac. Soc. Technol., vol. 13, 1976, p. 647, for example. A major disadvantage with such a design, especially for the growth of high-T.sub.c superconductors, is that most of the substrates of choice are transparent to visible light, and poor absorbers of infrared radiation. Without an intermediate heat absorber, this method can result in very inefficient heating of the substrates, and also very large errors in thermometry, especially if pyrometric temperature measurement techniques are relied upon.
Thus, in accordance with this inventive concept a need has been recognized for a high temperature substrate heater for depositing thin films in an oxidizing atmosphere that heats by direct thermal conduction and which is resistant to oxidation at high temperatures.